There has been sporadic interest in cement concretes as electrical insulators since about 1952. Recently, this interest has quickened due mainly to economic pressures brought about by the rise of costs of conventional porcelain and epoxy insulators.
One of the major problems in using concrete as an electrical insulator results from the fact that when the cement is mixed with the aggregate and water, air is of necessity entrained in the mixture. For example, normal Portland cements will entrain from 0.25 to 1.3 percent by volume of air. Of course, some cements are purposely formulated to entrain air, but for electrical insulation purposes, the air entrained in the concrete should be eliminated. Normally, the air pockets are not inter-connected as shown in FIG. 1, which is a photomicrograph of a white Portland cement concrete at 10.times. magnification. However, as the concrete ages, cracks often develop between the air pockets, as shown in FIG. 2, which is a photomicrograph of a white Portland cement concrete at 20.times. magnification. Obviously, the inter-connection of the electrically conducting air pockets caused by the cracks renders the concrete inappropriate for insulating applications.
Accordingly, it is the object of this invention to prepare an electrical grade concrete in which the air pockets usually inherent in the concrete will be eliminated.